Control method of laundry machine

ABSTRACT

A control method of a laundry machine is disclosed. The control method of a laundry machine comprising a balancer includes a step configured to determine an irregular vibration region of the laundry machine and a balancing step implemented at least one time before a rotation speed of a drum enters the irregular vibration region, while the rotation speed is passing the irregular vibration region and after the rotation speed passes the irregular vibration region.

TECHNICAL FIELD

The present invention relates to a control method of a laundry machine.

BACKGROUND ART

In general, a laundry machine may include washing, rinsing and spinning cycles. Here, the spinning cycle includes a rotating step of rotating a drum provided in such a laundry machine at the highest RPM. Because of the step, the spinning cycle would generate noise and vibration quite a lot, which is required to be solved in the art the prevent invention pertains to.

DISCLOSURE OF INVENTION Technical Problem

A method is provided for a rotation speed of a drum of a laundry machine to pass a transient region while reducing vibration of the drum in a case the drum is to be rotated to exceed the transient region in a laundry machine.

Particularly, a method is provided for a rotation speed of a drum of a laundry machine to pass a transient region while reducing vibration intensity of the drum when the transient region is over a comparatively wide range of a rotation speed of the drum.

Along with this, a method is provided for a rotation speed of a drum of a laundry machine to pass a transient region while reducing vibration intensity of the drum of the laundry machine of a new structure in which a tub is fixedly secured such that vibration of the drum is directly buffered by a suspension unit without passing through the tub.

Solution to Problem

To solve the problems, an object of the present invention is to provide a control method of a laundry machine comprising a balancer, the control method comprising a step configured to determine an irregular vibration region of the laundry machine and a balancing step implemented at least one time before a rotation speed of a drum enters the irregular vibration region, while the rotation speed is passing the irregular vibration region and after the rotation speed passes the irregular vibration region.

Advantageous Effects of Invention

The present invention has following advantageous effects.

In a case the drum is rotated to exceed the transient region, the rotation speed of the drum can pass through the transient region while reducing vibration of the drum, effectively.

Particularly, when the transient region is over a comparatively wide range of the rotation speed of the drum, the rotation speed of the drum can pass through the transient region while reducing vibration of the drum, effectively.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 5 illustrates a sch The accompanying drawings, which are included to provide further understanding of the disclosure and are incorporated in and constitute a part of this application, illustrate embodiments of the disclosure and together with the description serve to explain the principle of the disclosure.

In the drawings:

FIG. 1 illustrates an exploded perspective view of a laundry machine in accordance with a preferred embodiment of the present invention.

FIG. 2 illustrates a partial section of the laundry machine in FIG. 1.

FIG. 3 illustrates a section of a front balancer.

FIG. 4 illustrates a graph showing a relation of mass vs. a natural frequency. ematic view of a relation of an unbalance versus positions of balls as the drum rotates.

FIG. 6 illustrates a schematic view of a spinning method in accordance with a preferred embodiment of the present invention.

FIG. 7 illustrates a graph illustrating vibration characteristics of the laundry machine of FIG. 2.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a partial exploded perspective view illustrating a laundry machine according to one embodiment of the present invention.

According to a laundry machine according to an embodiment, the tub may be fixedly supported to the cabinet or it may be supplied to the cabinet by a flexible supporting structure such as a suspension unit which will be described later. Also, the supporting of the tub may be between the supporting of the suspension unit and the completely fixed supporting.

That is, the tub may be flexibly supported by the suspension unit which will be described later or it may be complete-fixedly supported to be movable more rigidly. Although not shown in the drawings, the cabinet may not be provided unlike embodiments which will be described later. For example, in case of a built-in type laundry machine, a predetermined space in which the built-in type laundry machine will be installed may be formed by a wall structure and the like, instead of the cabinet. In other words, the built-in type laundry machine may not include a cabinet configured to define an exterior appearance thereof independently.

The laundry machine according to this embodiment of the present invention includes a tub fixedly supported to a cabinet. The tub includes a tub front 100 configured to define a front part thereof and a tub rear 120 configured to define a rear part thereof. The tub front 100 and the tub rear 120 are assembled to each other by screws and a predetermined space is formed in the assembled structure to accommodate a drum. The tub rear 120 may include an opening formed in a rear surface thereof and an inner circumference of the rear surface of the tub rear 120 is connected with an outer circumference of a rear gasket 250. An inner circumference of the rear gasket 250 is connected with a tub back 130. The tub back 130 includes a through-hole formed in a center thereof and a shaft passes the through-hole. The rear gasket 250 may be made of flexible material not to transmit the vibration of the tub back 130 to the tub rear 120.

The tub rear 120 includes a rear surface 128. The rear surface 128 of the tub rear 120, the tub back 130 and the rear gasket 250 define a rear wall of the tub. The rear gasket 250 is sealingly connected with the tub back 130 and the tub rear 120 and it prevents wash water held in the tub from leaking out. The tub back 130 is vibrated together with the drum during the rotation of the drum. At this time, the tub back 130 is spaced apart from the tub rear 120 at a predetermined distance enough not to interfere with the tub rear 120. Since the rear gasket 250 is made of a flexible material, it allows the tub back 130 to relative-move without interfering with the tub rear 120. The rear gasket 250 may include a corrugation part 252 extendible enough to allow such a relative movement of the tub back 130.

A foreign-substance-preventing member 200 is connected with a front portion of the tub front 100 to prevent foreign substances from coming between the tub and the drum. The foreign-substance-preventing member 200 is made of a flexible material and it is fixedly installed to the tub front 100. The foreign-substance-preventing member 200 may be made of the same material as that used to make the rear gasket 250 and it will be referenced to as front gasket for convenience sake.

The drum includes a drum front 300, a drum center 320 and a drum back 340. Balancers 310 and 330 are installed in front and rear portions of the drum, respectively. The drum back 340 is connected with a spider 350, and the spider 350 is connected with a rotational shaft 351. The drum 32 is rotated in the tub by the rotational force transmitted via the rotational shaft 351.

The rotational shaft 351 is directly connected with a motor by passing through the tub back 130. Specifically, the rotational shaft 351 is directly connected with a rotor of the motor. A bearing housing 400 is coupled to a rear surface of the tub back 130. The bearing housing 400 is located between the motor and the tub back 130 to rotatably support the rotational shaft 351.

A stator is fixedly installed to the bearing housing 400 and the rotor is located around the stator. As mentioned above, the rotor is directly connected with the rotational shaft 351. The motor is an outer rotor type motor and it is directly connected with the rotational shaft 351.

The bearing housing 400 is supported from a cabinet base 600 through a suspension unit. The suspension unit includes three perpendicular supporting suspensions and two oblique-supporting suspensions configured to support the bearing housing obliquely in a forward and rearward direction.

The suspension unit may include a first cylinder spring 520, a second cylinder spring 510, a third cylinder spring 500, a first cylinder damper, and a second cylinder damper 530, wherein the first cylinder damper, although not shown, is symmetrically installed to be opposite to the second cylinder damper.

The first cylinder spring 520 is connected between a first suspension bracket 450 and the cabinet base 600, and the second cylinder spring 510 is connected between a second suspension bracket 440 and the cabinet base 600.

The third cylinder spring 500 is directly connected between the bearing housing 400 and the cabinet base 600.

The first cylinder damper 540 is obliquely installed between the first suspension bracket 450 and a rear portion of the cabinet base. The second cylinder damper 530 is obliquely installed between the second suspension bracket 440 and the rear portion of the cabinet base.

The cylinder springs 520, 510 and 500 of the suspension unit may be connected to the cabinet base 600 flexibly enough to allow the drum to move in a forward-and-rearward direction and a rightward-and-leftward direction, not completely fixed to the cabinet base 600. That is, the cylinder springs 520, 510 and 500 elastically support the drum to allow the drum to rotate vertically and horizontally with respect to the connected point with the cabinet base.

The perpendicular ones of the suspensions suspend the vibration of the drum elastically and the oblique ones dampen the vibration. That is, out of the vibration system that includes springs and damping means, the perpendicularly installed ones are employed as springs and the obliquely installed ones are employed as damping means.

The tub front and the tub rear are fixedly secured to the cabinet and the vibration of the drum is suspendingly supported by the suspension unit. Substantially, the structure of the tub and the drum may be separate. Even when the drum is vibrated, the tub may not be vibrated structurally.

The bearing housing and the suspension brackets are connected by first and second weights 431 and 430.

Hereinafter, a balancer will be described in more detail.

First of all, if the drum is rotated in a state that laundry is placed in the drum, unbalance may be generated by the laundry. Since such unbalance may cause high vibration of the drum during a spinning cycle, it is preferably required to reduce such unbalance (UB). In particular, as the rotation speed of the drum is increased, it reaches a natural vibration region of the laundry machine. In this case, a problem may occur in that the vibration becomes great if unbalance is too great.

Since it is impossible to uniformly distribute the laundry inside the drum, it is important to reduce unbalance if possible. An allowable unbalance rate may be required for the laundry machine considering characteristics of the laundry machine. In this respect, it is required to sense unbalance and compare the sensed unbalance with allowable unbalance to control rotation of the drum.

In order to reduce unbalance, several solutions may be provided. One of the several solutions is laundry distribution or uniform laundry distribution for varying the position of the laundry inside the drum.

Also, in order to reduce unbalance, a fluid may be located in an opposite position of an unbalanced position of the laundry to compensate for unbalance of the laundry. In other words, a balancer may be used.

In this embodiment, a ball balancer is used as the balancer. The balancer is respectively used at the front and rear portions of the drum.

In this embodiment, as shown in FIG. 2, the front balancer 310 is provided at the front portion of the drum, and the rear balancer 330 is provided at the rear portion of the drum. In more detail, the front balancer 310 is mounted on a front surface of the drum front 300, and the rear balancer 330 is mounted on a rear surface of the drum back 340. To this end, the drum front 300 may have a front recess recessed in a rearward direction on the front surface, and the drum back 340 may have a rear recess recessed in a forward direction.

In this embodiment, although not necessarily required, it is preferably required that the front balancer 310 is structurally the same as the rear balancer 330.

FIG. 3 illustrates a sectional structure of the front balancer 310.

First of all, the front balancer 310 includes a race 31, a ball 32, and an oil 33. The race 31 may have a ring shaped ball space portion 31 a where the ball 32 can move therein. The ball space portion 31 a may have a square shape roughly as shown.

A plurality of balls 32 are received in the ball space portion 31 a. The number of balls received in the ball space portion 31 a and a diameter of the ball are defined considering the unbalance rate, together with vibration characteristics of the laundry machine.

Also, since the ball space portion 31 a is filled with the oil 33, the number and diameter of balls received in the ball space portion 31 a are preferably defined considering the amount and viscosity of the oil 33, which affect movement of the ball 32. The amount and viscosity of the oil 33 may be determined such that the ball 32 of the balancer may have required movement. Also, the amount and viscosity of the oil 33 may be determined considering vibration characteristics of the laundry machine.

In this embodiment, 14 balls 32 are received in the ball space portion 31 a, and each of the balls has a diameter of 18.55 mm to 19.55 mm, preferably 19.05 mm. The ball space portion 31 a of the race has a sectional area in the range of 410 mm² to 413 mm², preferably 412 mm². A center diameter of the sectional area of the ball space portion 31 a is in the range of 500 mm to 510 mm, preferably 505 mm. Silicon based oil such as Poly Dimethylsiloxane (PDMS) is used as the oil 33. Preferably, the oil 33 has viscosity of 300 cs at a room temperature, and has a filling level of 340 cc to 360 cc, preferably 350 cc. It is to be understood that the present invention is not limited to the aforementioned characteristic values of the balancer.

Hereinafter, a method of using movement of the ball inside the balancer when the drum is rotated with unbalance will be described. Since the balancer is mounted on the drum and then rotated together with the drum, movement of the ball inside the balancer can be controlled finally by rotation control of the drum.

In particular, if the rotation speed of the drum is close to natural vibration of the laundry machine, the vibration of the drum may occur seriously. In this case, it is important how the ball is controlled.

In the laundry machine according to the related art, a natural vibration mode occurs in the range of 200 rpm to 270 rpm. Such a period where the natural vibration mode occurs may be referred to as a transient region. In this transient region, a plurality of natural vibration modes may exist. If the drum should be rotated at a rotation speed more than the transient region, it is important to control the ball such that the vibration of the drum becomes low.

Generally, the transient region may be defined as a rotation speed range of the drum. As described above, the transient region may be defined as a region that includes natural vibration. In the vibration system, natural vibration is determined by mass and rigidity (for example, spring constant). Since mass may be varied depending on the amount of laundry in the laundry machine, the transient region is preferably controlled considering mass.

FIG. 4 illustrates a graph showing a relation of mass vs. a natural frequency. It is assumed that, in vibration systems of two laundry machines, the two laundry machines have mass of m0 and m1 respectively and maximum holding laundry amounts are Δm, respectively. Then, the transition regions of the two laundry machines can be determined taking Δnf0 and Δnf1 into account, respectively. In this instance, amounts of water contained in the laundry will not be taken into account, for the time being.

In the meantime, referring to FIG. 4, the laundry machine with smaller mass m1 has a range of the transition region greater than the laundry machine with greater mass m0. That is, the range of the transition region having variation of the laundry amount taken into account becomes the greater as the mass of the vibration system becomes the smaller.

The ranges of the transition regions will be reviewed on the related art laundry machine and the laundry machine of the embodiment.

The related art laundry machine has a structure in which vibration is transmitted from the drum to the tub as it is, causing the tub to vibrate. Therefore, in taking the vibration of the related art laundry machine into account, the tub is indispensible. However, in general, the tub has, not only a weight of its own, but also substantial weights at a front, a rear or a circumferential surface thereof for balancing. Accordingly, the related art laundry machine has great mass of the vibration system.

Opposite to this, in the laundry machine of the embodiment, since the tub, not only has no weight, but also is separated from the drum in view of a supporting structure, the tub may not be put into account in consideration of the vibration of the drum. Therefore, the laundry machine of the embodiment may have relatively small mass of the vibration system.

Then, referring to FIG. 4, the related art laundry machine has mass m0 and the laundry machine of the embodiment has mass m1, leading the laundry machine of the embodiment to have a greater transition region, at the end.

Moreover, if the amounts of water contained in the laundry are taken into account simply, Δm in FIG. 4 will become greater, making a range difference of the transition regions even greater. And, since, in the related art laundry machine, the water drops into the tub from the drum even if the water escapes from the laundry as the drum rotates, an amount of water mass reduction come from the spinning is small. Since the laundry machine of the embodiment has the tub and the drum separated from each other in view of vibration, the water escaped from the drum influences the vibration of the drum, instantly. That is, the influence of a mass change of the water in the laundry is greater in the laundry machine of the embodiment than the related art laundry machine.

Under above reason, though the related art laundry machine has the transition region of about 200˜270 rpm, A start RPM of the transient region of the laundry machine according to this embodiment may be similar to a start RPM of the transient region of the conventional laundry machine. An end RPM of the transient region of the laundry machine according to this embodiment may increase more than a RPM calculated by adding a value of approximately 30% of the start RPM to the start RPM. For example, the transient region finishes at an RPM calculated by adding a value of approximately 80% of the start RPM to the start RPM. According to this embodiment, the transient region may include a RPM band of approximately 200 to 350 rpm.

In the meantime, by reducing intensity of the vibration of the drum, unbalance may be reduced. For this, even laundry spreading is performed for spreading the laundry in the drum as far as possible before the rotation speed of the drum enters into the transition region.

In a case, a balancer is used, a method may be put into account, in which the rotation speed of the drum passes through the transition region while movable bodies provided in the balancer are positioned on an opposite side of an unbalance of the laundry. In this instance, it is preferable that the movable bodies are positioned at exact opposite of the unbalance in middle of the transition region.

However, as described above, the transient region of the laundry machine according to this embodiment is relatively wide in comparison to that of the conventional laundry machine. Because of that, even if the laundry even-spreading step or ball balancing is implemented in a RPM band lower than the transient region, the laundry might be in disorder or balancing might be failed with the drum speed passing the transient region.

As a result, balancing may be implemented at least one time in the laundry machine according to this embodiment before and while the drum speed passing the transient region. Here, the balancing may be defined as rotation of the drum at a constant-speed for a predetermined time period. Such the balancing allows the movable body of the balancer to the opposite positions of the laundry, only to reduce the unbalance amount. By extension, the effect of the laundry even-spreading. Eventually, the balancing is implemented while the drum speed passing the transient region and the noise and vibration generated by the expansion of the transient region may be prevented.

Here, when the balancing is implemented before the drum speed passing the transient region, the balancing may be implemented in a different RPM band from the RPM of the conventional laundry machine. For example, if the transient region starts at 200 RPM, the balancing is implemented in the RPM band lower than approximately 150 RPM. Since the conventional laundry machine has a relatively less wide transient region, it is not so difficult for the drum speed to pass the transient region even with the balancing implemented at the RPM lower than approximately 150 RPM. However, the laundry machine according to this embodiment has the relatively wide expanded transient region as described above, if the balancing is implemented at the such the low RPM like in the conventional laundry machine, the positions of the movable bodies might be in disorder by the balancing implemented with the drum speed passing the transient region. Because of that, the laundry machine according to this embodiment may increase the balancing RPM in comparison to the conventional balancing RPM, when the balancing is implemented before the drum speed enters the transient region. That is, if the start RPM of the transient region is determined, the balancing is implemented in a RPM band higher than a RPM calculated by subtracting a value of approximately 25% of the start RPM from the start RPM. For example, the start RPM of the transient region is approximately 200 RPM, the balancing may be implemented in a RPM band higher than 150 RPM lower than 200 RPM.

Moreover, the unbalance amount may be measured during the balancing. That is, the control method may further include a step to measure the unbalance amount during the balancing and to compare the measured unbalance amount with an allowable unbalance amount allowing the acceleration of the drum speed. If the measured unbalance amount is less than the allowable unbalance amount, the drum speed is accelerated after the balancing to be out of the transient region. In contrast, if the measured unbalance amount is the allowable unbalance amount or more, the laundry even-spreading step may be re-implemented. In this case, the allowable unbalance amount may be different from an allowable unbalance amount allowing the initial accelerating.

A relation of the positions of the balls and the position of the unbalance may be defined as an angle of a center of centrifugal force of the balls (hereafter, a centrifugal force center angle) with respect to a center of the centrifugal force of the unbalance. Or, the relation of the positions of the balls and the position of the unbalance may be defined as an angle (hereafter, a closet ball angle) of a closest ball from the unbalance with respect to the center of the centrifugal force of the unbalance.

FIG. 5 illustrates a schematic view of a relation of unbalance UB versus ball positions as the drum rotates. In FIG. 5, of the relation of unbalance UB versus ball positions, the closest ball angle is θ1 and the centrifugal force center angle is θ2. For convenience' sake, a ball unbalance angle denotes θ1 or θ2.

The ball may be formed of steel, and if all of the balls are in contact with one another on a line, the centrifugal force center will be P1 shown in FIG. 5.

As the drum rotates, the balls rotate by friction with the drum. Since movement of the balls are not confined by the drum, the balls rotate at a speed different from the rotation speed of the drum. However, the unbalance, which is the laundry stuck to an inside of the drum, can rotate at a speed almost the same with the rotation speed of the drum owing to adequate friction and the lifts on the inside wall of the drum. Therefore, the rotation speed of the unbalance is different from the rotation speed of the balls. Since the balls rotate by rotation of the drum, the rotation speed of the unbalance is faster than the rotation speed of the balls. More specifically, an angular velocity is faster.

If the rotation speed of the drum becomes faster gradually, the balls come into close contact with an outside circumferential surface of a ball housing portion of a racer, by the centrifugal force. And, if the centrifugal force becomes greater, making friction between the circumferential surface and the balls to be greater than a certain value, the balls rotate at a rotation speed the same with the drum. In this case, the balls have fixed positions with respect to the drum the same as the unbalance. In the specification, for convenience' sake, a case when the balls rotate while the balls have the fixed positions with respect to the drum will be expressed as ‘balancing position’ or ‘balancing is done’.

A lowest rotation speed of the balancing speed can vary with the balancers, and with cases whether the balancer is mounted vertically, or horizontally. If the balancer is mounted vertically, contact of the balls with the outside circumferential surface of the ball housing portion of the racer can vary with positions due to gravity. If a constant rotation speed can be kept at a certain rotation speed at which the balancing can be made for a certain time period, the balls can be set at positions opposite to a position of the unbalance exactly, i.e., the P2 position in FIG. 5.

In the meantime, the balancing may fail at a rotation speed lower than the transient region due to low centrifugal force. Therefore, when it is intended to pass the transient region, rather than passing through the transient region after making the balancing, it is possible to position the balls on an opposite side of the unbalance during the rotation speed of the drum passes through the transient region by making the positions of the balls known while making the drum to rotate at a constant speed. That is, even if the balancing cannot be made, it is possible that the rotation speed passes through the transient region while the balls are positioned on the opposite side of the unbalance. For an example, referring to FIG. 5, it is possible that the rotation speed passes through the transient region while the angle θ1 or θ2 between the balls and the unbalance is 90° or greater than 90°. In this instance, it will be more preferable if the angle is 180° at middle of the transient region.

In the meantime, if the range of the transient region is wide such that the angle between the balls and the unbalance becomes less than 90° in a state the rotation speed does not pass the transient region yet, the vibration will become more intense as mass of the balls is added to the unbalance.

It is preferable that the angle between the balls and the unbalance is close to 180° for reducing the vibration even if the angle between the balls and the unbalance is not less than 90°.

Therefore, in a case the range of the transient region is wide like the laundry machine of the embodiment, it may not be preferable to pass the transient region with one time of acceleration.

A method for controlling a laundry machine to pass the transient region for performing spinning will be described by using a graph showing a relation of a time versus a rotation speed with reference to FIG. 6.

In FIG. 6, an a section denotes a first constant speed rotation step, a b section denotes a second constant speed rotation step, a c1 section denotes a first transient region step, a c2 section denotes a second transient region step, and a c3 section denotes a third transient region step.

In the a section, laundry spreading or laundry disentangling is performed, and a first unbalance is sensed while the drum makes constant speed rotation at the first rotation speed and the first unbalance is compared to a first allowable unbalance.

If the first unbalance sensed thus is below the first allowable unbalance, the drum is accelerated up to a second rotation speed and kept rotated at the second rotation speed (b section). In the b section, a second unbalance is sensed and compared to a second allowable balance. If the second unbalance sensed thus is below a second allowable unbalance, a preparation is made for passing the c section which is a transient region.

First, in order to pass the c1 section, positions of the balls are made known while rotating the drum at a constant speed, to determine an acceleration time point t1. In the c1 section, the t1 and an acceleration slope can be determined such that the angle between the unbalance and the balls are 90° or greater than 90°. In this instance, the t1 and the acceleration slope can be determined such that the angle between the unbalance and the balls is 180° at middle of the c1 section.

If the rotation speed of the drum passes through the c1 section and reaches to the third rotation speed, the drum is kept rotating at a constant speed for a preset time period (c2 section). In the c1 section, the angle between the unbalance and the balls passes the 180° such that the unbalance and the balls come closer gradually, again. Therefore, in the c2 section, while rotating in a constant speed, a preparation is made for passing through the c3 section which is a remained transient region.

The c2 section is a section in which the angle between the unbalance and the balls is made to increase again such that the rotation speed of the drum passes the c3 section in a state the angle between the unbalance and the balls is greater 90°, again.

In the c2 section, the angle between the unbalance and the balls can be smaller than 90°. However, as the constant speed is kept, the angle can be increased greater than 90°, again. In a state the angle between the unbalance and the balls is greater than 90°, the rotation speed of the drum is made to pass through the c3 section.

In this instance, the balancing can be made in the c2 section. That is, it is possible to maintain a state in which the angle between the unbalance and the balls to be 180°. For this, it is required to maintain the c2 section until the balancing is done. If it is intended not to make the balancing in the c2 section, it is preferable that a section is included to middle of the c2 section in which the angle between the unbalance and the balls is 180°.

If the balancing is done in the c2 section thus, since the vibration of the drum can become smaller further, it is preferable to make the balancing in the c2 section.

And, since there can be almost no change of the positions of the balls once the balancing is done in the c2 section thus, there can be nothing unnatural in passing the transient region even if the c3 section is wide. Therefore, the c3 section can have a range of the rotation speed greater than the c1 section. In other words, an inclination of rotation speed of C3 may be larger than that of C1

Moreover, since the positions of the balls are not required to be taken into account once the balancing is done in the c2 section, the rotation speed of the drum can pass the c3 section, quickly. Accordingly, the c3 section can have the acceleration slope steeper than the c1 section.

Since the balls are moving in the c1 section, if the rotation speed is increased too quickly, the vibration can become unstable.

In the meantime, it is preferable that the third rotation speed is determined such that the c1 section transits to the c2 section while vibration perpendicular to the rotation shaft of the drum becomes smaller, gradually.

Since the angle between the unbalance and the balls can even be less than 90° in c2 section, it is preferable the transition is performed in a state the vibration of the drum becomes small, adequately.

Accordingly, it is preferable that an average of intensity of the vibration of the drum in the c2 section is below maximum intensity of the vibration in the c1 section.

In the meantime, in determining the c2 section, it is preferable that the intensity of the vibration of the drum in the c3 section is smaller than the intensity of the vibration of the drum in the c1 section. Since the c3 section has the rotation speed higher than the c1 section, it is preferable that the c3 section has the intensity of the vibration of the drum smaller than the intensity of the vibration of the drum in the c1 section. It is preferable that maximum intensity of the vibration of the drum in the c3 section is below an half of the maximum intensity of the vibration of the drum in the c1 section.

Even though the embodiment takes performance of the spinning as an example, besides the spinning, the embodiment can also be applied to a case, if any, in which the drum is rotated exceeding the transient region.

First, vibration characteristics of the laundry machine according to the embodiment of the present invention will now be described with reference to FIG. 7.

As the rotation speed of the drum is increased, a region (hereinafter, referred to as”transient vibration region“) where irregular transient vibration with high amplitude occurs is generated. The transient vibration region irregularly occurs with high amplitude before vibration is transited to a steady-state vibration region (hereinafter, referred to as “steady-state region”), and has vibration characteristics determined if a vibration system (laundry machine) is designed. Though the transient vibration region is different according to the type of the laundry machine, transient vibration occurs approximately in the range of 200 rpm to 270 rpm. It is regarded that transient vibration is caused by resonance. Accordingly, it is necessary to design the balancer by considering effective balancing at the transient vibration region.

In the mean time, as described above, in the laundry machine according to the embodiment of the present invention, the vibration source, i.e., the motor and the drum connected with the motor are connected with the tub 12 through the rear gasket 250. Accordingly, vibration occurring in the drum is little forwarded to the tub, and the drum is supported by a damping means and the suspension unit 180 via a bearing housing 400. As a result, the tub 12 can directly be fixed to a cabinet 110 without any damping means.

As a result of studies of the inventor of the present invention, vibration characteristics not observed generally have been found in the laundry machine according to the present invention. According to the general laundry machine, vibration (displacement) becomes steady after passing through the transient vibration region. However, in the laundry machine according to the embodiment of the present invention, a region (hereinafter, referred to as“irregular vibration”) where vibration becomes steady after passing through the transient vibration region and again becomes great may be generated. For example, if the maximum drum displacement or more generated in an RPM band lower than the transient region or the maximum drum displacement or more of steady state step in a RPM band higher than the transient region is generated, it is determined that irregular vibration is generated. Alternatively, if an average drum displacement in the transient region, +20% to −20% of the average drum displacement in the transient region or ⅓ or more of the maximum drum displacement in the natural frequency of the transient region are generated, it may be determined that the irregular vibration is generated.

However, as a result of the studies, irregular vibration has occurred in a RPM band higher than the transient region, for example has occurred at a region (hereinafter, referred to as“irregular vibration region”) in the range of 350 rpm to 1000 rpm, approximately. Irregular vibration may be generated due to use of the balancer, the damping system, and the rear gasket. Accordingly, in this laundry machine, it is necessary to design the balancer by considering the irregular vibration region as well as the transient vibration region.

For example, the balancer is provide with a ball balancer, it is preferable that the structure of the balancer, i.e., the size of the ball, the number of balls, a shape of the race, viscosity of oil, and a filling level of oil are selected by considering the irregular vibration region as well as the transient vibration region. When considering the transient vibration region and/or the irregular vibration region, especially considering the irregular vibration region, the ball balancer has a greater diameter of 255.8 mm and a smaller diameter of 249.2. A space of the race, in which the ball is contained, has a sectional area of 411.93 mm². The number of balls is 14 at the front and the rear, respectively, and the ball has a size of 19.05 mm. Silicon based oil such as Poly Dimethylsiloxane (PDMS) is used as the oil. Preferably, oil has viscosity of 300 CS at a room temperature, and has a filling level of 350 cc.

In addition to the structure of the balancer, in view of control, it is preferable that the irregular vibration region as well as the transient vibration region is considered. For example, to prevent the irregular vibration, if the irregular vibration region is determined, the balancing may be implemented at least one time before, while and after the drum speed passes the irregular vibration region. Here, if the rotation speed of the drum is relatively high, the balancing of the balancer may not be implemented properly and the balancing may be implemented with decreasing the rotation speed of the drum. However, if the rotation speed of the drum is decreased to be lower than the transient region to implement the balancing, it has to pass the transient region again. In decreasing the rotation speed of the drum to implement the balancing, the decreased rotation speed may be higher than the transient region.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. 

1. A control method of a laundry machine comprising a drum having a balancer, the control method comprising: a step configured to balance the drum at least one time before and while a rotation speed of the drum passes a transient region.
 2. The control method as claimed in claim 1, wherein the transient region is defined as a RPM region between a start RPM and an end RPM more than a RPM calculated by adding a value of 30% of the start RPM to the start RPM.
 3. The control method as claimed in claim 1, wherein the transient region comprises a RPM band of 200 to 350 rpm.
 4. The control method as claimed in claim 1, wherein the balancing is implemented in a RPM band higher than a RPM calculated by subtracting a value of approximately 25% of the start RPM from the start RPM, if balancing is implemented before the drum speed passes the transient region.
 5. The control method as claimed in claim 4, wherein the balancing RPM is lower than the start RPM of the transient region.
 6. The control method as claimed in claim 1, wherein the balancing is implemented at a balancing RPM band of 150 RPM or higher and lower than 200 RPM before the drum speed passes the transient region.
 7. The control method as claimed in claim 1, wherein the laundry machine includes a balancer and the control method comprising: a first transient region step for starting acceleration of the drum in a state an angle between an unbalance and balls is 90° or greater than 90° to enter into a transient region; a third constant speed rotation step for rotating the drum at a constant speed of a third rotation speed to increase the angle between the unbalance and the balls again; and, a second transient region step for accelerating the drum to a rotation speed higher than the third rotation speed in a state the angle between the unbalance and the balls is 90° or greater than 90° for escaping from the transient region.
 8. The control method as claimed in claim 7, further comprising a first constant speed rotation step for rotating the drum at a constant speed rotation of a first rotation speed to sense a first unbalance and to compare the first unbalance to a first allowable unbalance.
 9. The control method as claimed in claim 7, wherein the third constant speed rotation step is maintained for a time period to make ball balancing of the balancer.
 10. The control method as claimed in claim 9, wherein an inclination of rotation speed of the second transient region step is larger than an inclination of rotation speed of the first transient region step.
 11. The control method as claimed in claim 9, wherein the laundry machine includes a balancer and the second transient region step has an acceleration slope steeper than the acceleration slope of the first transient region step.
 12. The control method as claimed in claim 7, wherein the third rotation speed is determined such that the first transient region step transits to the third constant speed rotation step while vibration perpendicular to the rotation shaft of the drum becomes smaller, gradually.
 13. The control method as claimed in claim 12, wherein the third rotation speed is determined such that an average of maximum intensity of the vibration of the drum in the third constant speed rotation step is below an half of the maximum intensity of the vibration of the drum in the first transient region step.
 14. The control method as claimed in claim 7, wherein the first transient region step includes a section in which the angle between the unbalance and the balls is 180°.
 15. The control method as claimed in claim 14, wherein the second transient region step includes a section in which the angle between the unbalance and the balls is 180°.
 16. The control method as claimed in claim 15, wherein the third constant speed rotation step is maintained for a time period to make balancing of the balancer.
 17. The control method as claimed in claim 7, wherein the second transient region step has a maximum intensity of vibration perpendicular to a rotation shaft of the drum below an half of the maximum intensity of the vibration in the first transient region step.
 18. The control method as claimed in claim 8, further comprising a second constant speed rotation step of sensing a second unbalance of the drum at a second rotation speed faster than the first rotation speed and comparing the second unbalance with a second allowable unbalance.
 19. The control method as claimed in claim 1, wherein the laundry machine comprises a driving unit comprising a shaft connected to a drum, a bearing housing to rotatably support the shaft, and a motor to rotate the shaft, and a suspension assembly is connected to the driving unit
 20. The control method as claimed in claim 1, wherein the laundry machine comprises a rear gasket for sealing to prevent washing water from leaking from a space between a driving unit and a tub, and enabling the driving unit movable relative to the tub.
 21. The control method as claimed in claim 1, wherein a tub is supported rigidly more than a drum being supported by a suspension assembly.
 22. The control method as claimed in claim 19, wherein the balancer includes; 14 balls each with a diameter of 18.55˜19.55 mm, and a racer with a ball housing portion which is a space for housing the balls with a sectional area of 410˜413 mm² and a diameter of 500˜510 mm.
 23. The control method as claimed in claim 19, wherein the ball housing portion of each of the front balancer and the rear balancer includes 340˜360 cc of oil with 300 cs viscosity injected thereto.
 24. The control method as claimed in claim 20, wherein the balancer includes; 14 balls each with a diameter of 18.55˜19.55 mm, and a racer with a ball housing portion which is a space for housing the balls with a sectional area of 410˜413 mm² and a diameter of 500˜510 mm.
 25. The control method as claimed in claim 21, wherein the balancer includes; 14 balls each with a diameter of 18.55˜19.55 mm, and a racer with a ball housing portion which is a space for housing the balls with a sectional area of 410˜413 mm² and a diameter of 500˜510 mm.
 26. The control method as claimed in claim 20, wherein the ball housing portion of each of the front balancer and the rear balancer includes 340˜360 cc of oil with 300 cs viscosity injected thereto.
 27. The control method as claimed in claim 21, wherein the ball housing portion of each of the front balancer and the rear balancer includes 340˜360 cc of oil with 300 cs viscosity injected thereto. 